As a technique for separating hydrogen from hydrogen mixed gases, a variety of methods such as PSA, deep freezing, chemical adsorption and separation membrane may be used.
Of the above technologies, a separation process using separation membranes is known to be the best in terms of energy efficiency. Recently, development of a separation process using hydrogen membranes to commercialize an extra-large refining portion such as pre-firing CCS (carbon capture and storage) is under way.
In order to have the above process completed, a module configuration technique, whereby high efficiency and durability can be provided so that first the hydrogen penetration speed and durability of the separation membrane itself are ensured and second the performance of separation membrane can be well displayed, is a key point.
There has been much research into module configuration for hydrogen refining using a separation membrane, and such research was conducted from the standpoint of securing high-concentration hydrogen that has penetrated the separation membrane.
However, in a separation membrane-applied process which needs to satisfy hydrogen refining and CO2 concentration simultaneously as in pre-firing CCS, it is not possible to obtain a concentration of residual gas at a certain level or more unless the recovery rate of hydrogen is maintained high. That is, when removing hydrogen from mixed gases, diffusion of material above the separation membrane acts as a dominant factor for the hydrogen removal efficiency of the separation membrane, because the concentration of hydrogen in residual gases that have not penetrated the separation membrane decreases gradually. Therefore, the configuration of the separation membrane exerts an absolute influence.
A unit module requires minimization of the mixed gas flow space so that the mass transfer resistance can be minimized according to the above configuration, and along with the unit cell having such a configuration, it requires a method of increasing the capacity of a module with a multistage configuration so that mixed gases can be supplied uniformly to each unit cell.
U.S. Pat. Nos. 6,319,305 and 5,997,594 disclose a unit module extension method. In the inventions of the above patents, since a gas supply unit is connected to a discharge unit through one communication hole, a difference in gas supply pressure transmitted according to the increase of the number of unit cells to be laminated may occur. Thus, as it becomes farther away from a supply hole, the feed rate of mixed gas supplied to the unit cell decreases gradually. Of course, such a problem can have its effect minimized by increasing the size of the communication hole infinitely, but as the unit module cross sectional area increases, the costs and size of the refining apparatus increase enormously to cause competitiveness to decrease by half.
Further, the above multilayered module can be sealed by diffusion bonding of the component plates or placing covers above and below the module and then fastening by a plurality of bolts. However, the above configuration makes it difficult to secure durability because expansion pressure is applied to the connecting part of the unit cell according to the supply of high-pressure mixed gas to the module. Especially in the case of pre-firing CCS, the pressure of the separation process is aimed at 68 bars as a development goal. Accordingly, development of a module that can endure high pressure is indispensable.
Further, recently a process, in which hydrogen from hydrogen mixed gas and the gas mixed in it need to be enriched to a certain concentration, is becoming increasingly popular. Typically in the case of the pre-firing CCS field, effort is being made for solving a technically intractable problem wherein the extent of enrichment of CO2, which is an impermeable gas, is to be satisfied simultaneously with the separation of hydrogen.